Polymeric microcapsules can be produced by one of several methods readily known in the art. Such methods include single and double emulsion solvent evaporation techniques.
Polymeric microcapsules have a wide variety of uses, such as use in drug delivery systems and personal care products, including dentifrices (i.e., a substance, such as a paste or powder, for cleaning the teeth). However, polymeric microcapsules generally do not provide good protection of an active ingredient encapsulated by the microcapsule from its external environment, such as one composed of a dentifrice formulation, while providing extended release of the active ingredient.
Cetylpyridinium chloride (CPC) is a cationic, surfactant-like, broad-spectrum antimicrobial agent that can be used for oral-care applications. However, due to its positive charge, CPC forms stable complexes with various common ingredients often used in, for example, dentifrices, such as sodium lauryl sulfate (SLS), an anionic surfactant. These types of reactions preclude the use of CPC in for example, common dentifrice formulations to deliver effective antimicrobial benefits.
In dentifrice applications, in order for microcapsules to stay intact during the toothpaste making and storage process, the microcapsules should possess the following properties: 1) good mechanical properties to sustain shear forces up to about 1000/s during mixing and high speed filling; 2) good temperature stability that allow the capsules to stay intact at temperatures up to about 71° C.; 3) good chemical stability that allows the capsules to be stable in the presence of sodium lauryl sulfate having a concentration of up to about 2% and a pH of about 5-8, and various water and humectants ratios. In addition, upon brushing, the microcapsules should break and release CPC to the oral cavity directly without formation of inactive complexes.
There are a number of triggers that allow the breakage of microcapsules during brushing, such as: 1) a mechanical trigger due to the grinding and shearing of toothbrush bristles; 2) a pH trigger due to the change in pH from a dentifrice base to an oral cavity environment; 3) an osmotic trigger due to the dilution of a dentifrice by saliva in the mouth during teeth brushing; and 4) an enzymatic trigger due to the breakage of polymer bonds by enzymes in the mouth.
It has also recently been recently reported in the literature that polymer microcapsules having mucoadhesive polymers has been formed via a water-in-oil emulsion method.
Accordingly, there is still a need for polymeric microcapsules that provide good protection of the active ingredient from its external environment while providing extended release profiles of the active ingredient over a significant period of time, such as a 24 hour time period. In addition, such polymeric microcapsules used in dentifrices, should have mucoadhesive properties that allow for extended release profiles of the active ingredient over a significant time period. In particular, there is still a need for an encapsulation technology to shield active ingredients, such as CPC, from incompatible ingredients, such as SLS.